1. Field of the Invention
This invention generally relates to a clutch actuated piston structure. More specifically, the present invention relates to a clutch actuated piston structure, which moves a piston by hydraulic oil to selectively engage and release a clutch engaging member. The clutch actuated piston structure is especially useful in a torque converter.
2. Background Information
Multi-disk clutches are often used in the transmissions of vehicles. Multi-disk clutches typically have a piston for engaging and releasing a clutch engaging member. In addition, a hydraulic chamber constructed from the piston and the hydraulic chamber structural member is disposed on the side opposite the clutch engaging member of the piston. When the hydraulic oil pressure is applied to the hydraulic chamber, the piston overcomes the driving force of a return spring to move towards the clutch engaging member and engage the clutch. When the application of hydraulic oil pressure to the hydraulic chamber is stopped, the piston returns to a given position by the driving force of the return spring and releases the clutch engaging member.
A check ball mechanism is sometimes provided in the multi-disk clutch as a hydraulic oil pressure exhaust mechanism, which releases the hydraulic oil pressure in the hydraulic chamber during movement of the piston to a clutch release position. The check ball mechanism typically includes an exhaust hole formed on the clutch side of the piston, a large-diameter hole formed on the hydraulic chamber side of the piston and passing through the exhaust hole, and a check ball disposed inside the large-diameter hole. The check ball can move between a first opened position where it is removed from the exhaust hole and a second closed position where it closes the exhaust hole. When working pressure is supplied to the hydraulic chamber, the check ball moves from the first opened position to the second closed position to cover the exhaust hole. Consequently, a large hydraulic oil pressure is produced in the hydraulic chamber. When working pressure is no longer provided in the hydraulic chamber, the check ball moves back to the first opened position by centrifugal force to uncover the exhaust hole. Thus, the hydraulic oil of the hydraulic chamber escapes through the exhaust port, and the piston is rapidly separated from the clutch engaging member.
When the flow rate of the hydraulic oil supplied to the hydraulic chamber is constant, the moving speed of the piston towards the clutch engaging member side, when the clutch is being engaged, is determined by the volume of the hydraulic chamber. Namely, if the volume of the hydraulic chamber is too large, the moving speed of the piston to the clutch engaging becomes slower. Therefore, starting the transmission torque of the clutch engaging member becomes slower.
Since the check ball is moved by centrifugal force, the action can be unstable. Therefore, the flow path area of the exhaust hole sometimes is not sufficiently guaranteed during the clutch release action. In addition, since the check ball is used, the exhaust hole cannot be too large. The reason the exhaust hole cannot be too large is that a very small part of the check ball covers the exhaust hole. Unfortunately, if the exhaust hole only becomes slightly larger, the check ball will become extremely large. Given the above results, the hydraulic oil pressure in the hydraulic chamber does not adequately escape during piston operation when the clutch is released. In this case, the return action of the piston becomes slower.
In view of the above, there exists a need for a clutch actuated piston structure which overcomes the problems in the prior art devices. This invention addresses these needs in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.